This compressor samples the cache for a while, trying to define the most frequently used values. More...

#include <frequent_values.hh>

Inheritance diagram for gem5::compression::FrequentValues:

Classes
class	CompData

class	FrequentValuesListener

class	VFTEntry

Public Types
typedef FrequentValuesCompressorParams	Params

Public Types inherited from gem5::compression::Base
typedef BaseCacheCompressorParams	Params

Public Types inherited from gem5::SimObject
typedef SimObjectParams	Params

Public Member Functions
	FrequentValues (const Params &p)

	~FrequentValues ()=default

void	probeNotify (const DataUpdate &data_update)
	Process a notification event from the ProbeListener.

void	regProbeListeners () override
	Register probe listeners for this object.

Public Member Functions inherited from gem5::compression::Base
	Base (const Params &p)

virtual	~Base ()=default

virtual void	setCache (BaseCache *_cache)
	The cache can only be set once.

std::unique_ptr< CompressionData >	compress (const uint64_t *data, Cycles &comp_lat, Cycles &decomp_lat)
	Apply the compression process to the cache line.

Cycles	getDecompressionLatency (const CacheBlk *blk)
	Get the decompression latency if the block is compressed.

Public Member Functions inherited from gem5::SimObject
const Params &	params () const

	SimObject (const Params &p)

virtual	~SimObject ()

virtual void	init ()
	init() is called after all C++ SimObjects have been created and all ports are connected.

virtual void	loadState (CheckpointIn &cp)
	loadState() is called on each SimObject when restoring from a checkpoint.

virtual void	initState ()
	initState() is called on each SimObject when not restoring from a checkpoint.

virtual void	regProbePoints ()
	Register probe points for this object.

ProbeManager *	getProbeManager ()
	Get the probe manager for this object.

virtual Port &	getPort (const std::string &if_name, PortID idx=InvalidPortID)
	Get a port with a given name and index.

virtual void	startup ()
	startup() is the final initialization call before simulation.

DrainState	drain () override
	Provide a default implementation of the drain interface for objects that don't need draining.

virtual void	memWriteback ()
	Write back dirty buffers to memory using functional writes.

virtual void	memInvalidate ()
	Invalidate the contents of memory buffers.

void	serialize (CheckpointOut &cp) const override
	Serialize an object.

void	unserialize (CheckpointIn &cp) override
	Unserialize an object.

Public Member Functions inherited from gem5::EventManager
EventQueue *	eventQueue () const

void	schedule (Event &event, Tick when)

void	deschedule (Event &event)

void	reschedule (Event &event, Tick when, bool always=false)

void	schedule (Event *event, Tick when)

void	deschedule (Event *event)

void	reschedule (Event *event, Tick when, bool always=false)

void	wakeupEventQueue (Tick when=(Tick) -1)
	This function is not needed by the usual gem5 event loop but may be necessary in derived EventQueues which host gem5 on other schedulers.

void	setCurTick (Tick newVal)

	EventManager (EventManager &em)
	Event manger manages events in the event queue.

	EventManager (EventManager *em)

	EventManager (EventQueue *eq)

Public Member Functions inherited from gem5::Serializable
	Serializable ()

virtual	~Serializable ()

void	serializeSection (CheckpointOut &cp, const char *name) const
	Serialize an object into a new section.

void	serializeSection (CheckpointOut &cp, const std::string &name) const

void	unserializeSection (CheckpointIn &cp, const char *name)
	Unserialize an a child object.

void	unserializeSection (CheckpointIn &cp, const std::string &name)

Public Member Functions inherited from gem5::Drainable
DrainState	drainState () const
	Return the current drain state of an object.

virtual void	notifyFork ()
	Notify a child process of a fork.

Public Member Functions inherited from gem5::statistics::Group
	Group (Group parent, const char name=nullptr)
	Construct a new statistics group.

virtual	~Group ()

virtual void	regStats ()
	Callback to set stat parameters.

virtual void	resetStats ()
	Callback to reset stats.

virtual void	preDumpStats ()
	Callback before stats are dumped.

void	addStat (statistics::Info *info)
	Register a stat with this group.

const std::map< std::string, Group * > &	getStatGroups () const
	Get all child groups associated with this object.

const std::vector< Info * > &	getStats () const
	Get all stats associated with this object.

void	addStatGroup (const char name, Group block)
	Add a stat block as a child of this block.

const Info *	resolveStat (std::string name) const
	Resolve a stat by its name within this group.

void	mergeStatGroup (Group *block)
	Merge the contents (stats & children) of a block to this block.

	Group ()=delete

	Group (const Group &)=delete

Group &	operator= (const Group &)=delete

Public Member Functions inherited from gem5::Named
	Named (const std::string &name_)

virtual	~Named ()=default

virtual std::string	name () const

Private Types
enum	Phase { SAMPLING , CODE_GENERATION , COMPRESSING }
	The phase that the compressor is at. More...

using	DataUpdate = CacheDataUpdateProbeArg

Private Member Functions
void	sampleValues (const std::vector< uint64_t > &data, bool is_invalidation)
	Sample values from a packet, adding them to the VFT.

void	generateCodes ()
	End sampling phase and start the code generation.

std::unique_ptr< Base::CompressionData >	compress (const std::vector< Chunk > &chunks, Cycles &comp_lat, Cycles &decomp_lat) override
	Apply the compression process to the cache line.

void	decompress (const CompressionData comp_data, uint64_t data) override
	Apply the decompression process to the compressed data.

Private Attributes
std::vector< FrequentValuesListener * >	listeners

const bool	useHuffmanEncoding
	Whether Huffman encoding is applied to the VFT indices.

encoder::Huffman	indexEncoder
	The encoder applied to the VFT indices.

const int	counterBits
	Number of bits in the saturating counters.

const Tick	codeGenerationTicks
	Ticks needed to perform the CODE_GENERATION phase.

const bool	checkSaturation
	Whether an action must be performed when counters saturate.

const unsigned	numVFTEntries
	Maximum number of VFT entries, and thus of codewords too.

const unsigned	numSamples
	Number of samples in the sampling phase.

unsigned	takenSamples
	Number of samples taken so far.

Phase	phase

AssociativeCache< VFTEntry >	VFT
	The Value Frequency Table, a small cache that keeps track and estimates the frequency distribution of values in the cache.

uint64_t	uncompressedValue
	A pseudo value is used as the representation of uncompressed values.

EventFunctionWrapper	codeGenerationEvent
	Event to handle finishing code generation and starting compression.

Additional Inherited Members
Static Public Member Functions inherited from gem5::compression::Base
static void	setDecompressionLatency (CacheBlk *blk, const Cycles lat)
	Set the decompression latency of compressed block.

static void	setSizeBits (CacheBlk *blk, const std::size_t size_bits)
	Set the size of the compressed block, in bits.

Static Public Member Functions inherited from gem5::SimObject
static void	serializeAll (const std::string &cpt_dir)
	Create a checkpoint by serializing all SimObjects in the system.

static SimObject *	find (const char *name)
	Find the SimObject with the given name and return a pointer to it.

static void	setSimObjectResolver (SimObjectResolver *resolver)
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.

static SimObjectResolver *	getSimObjectResolver ()
	There is a single object name resolver, and it is only set when simulation is restoring from checkpoints.

Static Public Member Functions inherited from gem5::Serializable
static const std::string &	currentSection ()
	Gets the fully-qualified name of the active section.

static void	generateCheckpointOut (const std::string &cpt_dir, std::ofstream &outstream)
	Generate a checkpoint file so that the serialization can be routed to it.

Protected Types inherited from gem5::compression::Base
typedef uint64_t	Chunk
	A chunk is a basic lexical unit.

Protected Member Functions inherited from gem5::compression::Base
std::vector< Chunk >	toChunks (const uint64_t *data) const
	This function splits the raw data into chunks, so that it can be parsed by the compressor.

void	fromChunks (const std::vector< Chunk > &chunks, uint64_t *data) const
	This function re-joins the chunks to recreate the original data.

Protected Member Functions inherited from gem5::Drainable
	Drainable ()

virtual	~Drainable ()

virtual void	drainResume ()
	Resume execution after a successful drain.

void	signalDrainDone () const
	Signal that an object is drained.

Protected Attributes inherited from gem5::compression::Base
const std::size_t	blkSize
	Uncompressed cache line size (in bytes).

const unsigned	chunkSizeBits
	Chunk size, in number of bits.

const std::size_t	sizeThreshold
	Size in bytes at which a compression is classified as bad and therefore the compressed block is restored to its uncompressed format.

const Cycles	compChunksPerCycle
	Degree of parallelization of the compression process.

const Cycles	compExtraLatency
	Extra latency added to compression due to packaging, shifting or other operations.

const Cycles	decompChunksPerCycle
	Degree of parallelization of the decompression process.

const Cycles	decompExtraLatency
	Extra latency added to decompression due to packaging, shifting or other operations.

BaseCache *	cache
	Pointer to the parent cache.

gem5::compression::Base::BaseStats	stats

Protected Attributes inherited from gem5::SimObject
const SimObjectParams &	_params
	Cached copy of the object parameters.

Protected Attributes inherited from gem5::EventManager
EventQueue *	eventq
	A pointer to this object's event queue.

Detailed Description

This compressor samples the cache for a while, trying to define the most frequently used values.

When these values are determined, they are associated to shorter representations (codes). Then the compressor can start its effective compression phase, in which occurrences of these values are substituted by their codes.

Definition at line 62 of file frequent_values.hh.

Member Typedef Documentation

◆ DataUpdate

using gem5::compression::FrequentValues::DataUpdate = CacheDataUpdateProbeArg

private

Definition at line 67 of file frequent_values.hh.

◆ Params

typedef FrequentValuesCompressorParams gem5::compression::FrequentValues::Params

Definition at line 181 of file frequent_values.hh.

Member Enumeration Documentation

◆ Phase

enum gem5::compression::FrequentValues::Phase

private

The phase that the compressor is at.

It assumes that sampling and code generation are done only once.

Enumerator
SAMPLING
CODE_GENERATION
COMPRESSING

Definition at line 112 of file frequent_values.hh.

Constructor & Destructor Documentation

◆ FrequentValues()

gem5::compression::FrequentValues::FrequentValues ( const Params & p )

Definition at line 48 of file frequent_values.cc.

References COMPRESSING, and phase.

◆ ~FrequentValues()

gem5::compression::FrequentValues::~FrequentValues ( )

default

Member Function Documentation

◆ compress()

std::unique_ptr< Base::CompressionData > gem5::compression::FrequentValues::compress	(	const std::vector< Chunk > &	chunks,
		Cycles &	comp_lat,
		Cycles &	decomp_lat )

overrideprivatevirtual

Apply the compression process to the cache line.

Returns the number of cycles used by the compressor, however it is usually covered by a good pipelined execution, and is currently ignored. The decompression latency is also returned, in order to avoid increasing simulation time and memory consumption.

Parameters

chunks	The cache line to be compressed, divided into chunks.
comp_lat	Compression latency in number of cycles.
decomp_lat	Decompression latency in number of cycles.

Returns: Cache line after compression.

Implements gem5::compression::Base.

Definition at line 64 of file frequent_values.cc.

References gem5::compression::Base::chunkSizeBits, gem5::compression::encoder::Code::code, gem5::compression::Base::compChunksPerCycle, gem5::compression::Base::compExtraLatency, COMPRESSING, gem5::compression::Base::decompChunksPerCycle, gem5::compression::Base::decompExtraLatency, DPRINTF, gem5::compression::encoder::Huffman::encode(), gem5::MipsISA::index, indexEncoder, gem5::compression::encoder::Code::length, numVFTEntries, phase, uncompressedValue, useHuffmanEncoding, and VFT.

◆ decompress()

void gem5::compression::FrequentValues::decompress	(	const CompressionData *	comp_data,
		uint64_t *	cache_line )

overrideprivatevirtual

Apply the decompression process to the compressed data.

Parameters

comp_data	Compressed cache line.
cache_line	The cache line to be decompressed.

Implements gem5::compression::Base.

Definition at line 137 of file frequent_values.cc.

References gem5::compression::encoder::Code::code, gem5::compression::FrequentValues::CompData::compressedValues, COMPRESSING, data, DPRINTF, gem5::compression::encoder::Huffman::encode(), gem5::compression::Base::fromChunks(), indexEncoder, gem5::compression::encoder::Code::length, phase, uncompressedValue, useHuffmanEncoding, and VFT.

◆ generateCodes()

void gem5::compression::FrequentValues::generateCodes ( )

private

End sampling phase and start the code generation.

Definition at line 218 of file frequent_values.cc.

References CODE_GENERATION, codeGenerationEvent, codeGenerationTicks, gem5::curTick(), gem5::compression::encoder::Huffman::generateCodeMaps(), gem5::ArmISA::i, indexEncoder, numVFTEntries, phase, gem5::compression::encoder::Huffman::sample(), gem5::EventManager::schedule(), uncompressedValue, useHuffmanEncoding, and VFT.

Referenced by probeNotify().

◆ probeNotify()

void gem5::compression::FrequentValues::probeNotify ( const DataUpdate & data_update )

Process a notification event from the ProbeListener.

Parameters

data_update The data regarding the entry's contents update.

Definition at line 265 of file frequent_values.cc.

References generateCodes(), gem5::CacheDataUpdateProbeArg::newData, numSamples, gem5::CacheDataUpdateProbeArg::oldData, phase, sampleValues(), SAMPLING, and takenSamples.

Referenced by gem5::compression::FrequentValues::FrequentValuesListener::notify().

◆ regProbeListeners()

void gem5::compression::FrequentValues::regProbeListeners ( )

overridevirtual

Register probe listeners for this object.

No probe listeners by default, so do nothing in base.

Reimplemented from gem5::SimObject.

Definition at line 289 of file frequent_values.cc.

References gem5::compression::Base::cache, gem5::SimObject::getProbeManager(), and listeners.

◆ sampleValues()

void gem5::compression::FrequentValues::sampleValues	(	const std::vector< uint64_t > &	data,
		bool	is_invalidation )

private

Sample values from a packet, adding them to the VFT.

Parameters

data	The line being sampled.
is_invalidation	whether this event comes from an invalidation.

Definition at line 177 of file frequent_values.cc.

References checkSaturation, gem5::compression::FrequentValues::VFTEntry::counter, data, gem5::GenericSatCounter< T >::isSaturated(), takenSamples, gem5::compression::Base::toChunks(), gem5::compression::FrequentValues::VFTEntry::value, and VFT.

Referenced by probeNotify().

Member Data Documentation

◆ checkSaturation

const bool gem5::compression::FrequentValues::checkSaturation

private

Whether an action must be performed when counters saturate.

Definition at line 97 of file frequent_values.hh.

Referenced by sampleValues().

◆ codeGenerationEvent

EventFunctionWrapper gem5::compression::FrequentValues::codeGenerationEvent

private

Event to handle finishing code generation and starting compression.

Definition at line 160 of file frequent_values.hh.

Referenced by generateCodes().

◆ codeGenerationTicks

const Tick gem5::compression::FrequentValues::codeGenerationTicks

private

Ticks needed to perform the CODE_GENERATION phase.

Definition at line 94 of file frequent_values.hh.

Referenced by generateCodes().

◆ counterBits

const int gem5::compression::FrequentValues::counterBits

private

Number of bits in the saturating counters.

Definition at line 91 of file frequent_values.hh.

◆ indexEncoder

encoder::Huffman gem5::compression::FrequentValues::indexEncoder

private

The encoder applied to the VFT indices.

Definition at line 88 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ listeners

std::vector<FrequentValuesListener*> gem5::compression::FrequentValues::listeners

private

Definition at line 82 of file frequent_values.hh.

Referenced by regProbeListeners().

◆ numSamples

const unsigned gem5::compression::FrequentValues::numSamples

private

Number of samples in the sampling phase.

Definition at line 103 of file frequent_values.hh.

Referenced by probeNotify().

◆ numVFTEntries

const unsigned gem5::compression::FrequentValues::numVFTEntries

private

Maximum number of VFT entries, and thus of codewords too.

Definition at line 100 of file frequent_values.hh.

Referenced by compress(), and generateCodes().

◆ phase

Phase gem5::compression::FrequentValues::phase

private

Definition at line 113 of file frequent_values.hh.

Referenced by compress(), decompress(), FrequentValues(), generateCodes(), and probeNotify().

◆ takenSamples

unsigned gem5::compression::FrequentValues::takenSamples

private

Number of samples taken so far.

Definition at line 106 of file frequent_values.hh.

Referenced by probeNotify(), and sampleValues().

◆ uncompressedValue

uint64_t gem5::compression::FrequentValues::uncompressedValue

private

A pseudo value is used as the representation of uncompressed values.

This value is a random value that is not present in the VFT. It is selected at the end of the sampling phase.

Definition at line 157 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ useHuffmanEncoding

const bool gem5::compression::FrequentValues::useHuffmanEncoding

private

Whether Huffman encoding is applied to the VFT indices.

Definition at line 85 of file frequent_values.hh.

Referenced by compress(), decompress(), and generateCodes().

◆ VFT

AssociativeCache<VFTEntry> gem5::compression::FrequentValues::VFT

private

The Value Frequency Table, a small cache that keeps track and estimates the frequency distribution of values in the cache.

Definition at line 150 of file frequent_values.hh.

Referenced by compress(), decompress(), generateCodes(), and sampleValues().

The documentation for this class was generated from the following files:

mem/cache/compressors/frequent_values.hh
mem/cache/compressors/frequent_values.cc

Classes

Public Types

Public Member Functions

Private Types

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Member Typedef Documentation

◆ DataUpdate

◆ Params

Member Enumeration Documentation

◆ Phase

Constructor & Destructor Documentation

◆ FrequentValues()

◆ ~FrequentValues()

Member Function Documentation

◆ compress()

◆ decompress()

◆ generateCodes()

◆ probeNotify()

◆ regProbeListeners()

◆ sampleValues()

Member Data Documentation

◆ checkSaturation

◆ codeGenerationEvent

◆ codeGenerationTicks

◆ counterBits

◆ indexEncoder

◆ listeners

◆ numSamples

◆ numVFTEntries

◆ phase

◆ takenSamples

◆ uncompressedValue

◆ useHuffmanEncoding

◆ VFT